semctl

first to get the correct constant definitions. If CMD is IPC_STAT or
GETALL, then ARG must be a variable that will hold the returned
semid_ds structure or semaphore value array. Returns like ioctl:
the undefined value for error, "0 but true" for zero, or the actual
return value otherwise. The ARG must consist of a vector of native
short integers, which may be created with pack("s!",(0)x$nsem).
See also SysV IPC in perlipc, IPC::SysV
, IPC::Semaphore
documentation.

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